The Seoul Capital Area has a population of 25.6 million (as of 2012)[1] and is ranked as the second largest metropolitan area in the world. Its area is about 11,704km2. It forms the cultural, commercial, financial, industrial, and residential center of South Korea. The largest city is Seoul, with a population of approximately 10.49 million people, followed by Incheon, with 2.8 million.

The Capital Area occupies a plain in the Han River valley. It contains some of the most fertile land on the Korean peninsula, although relatively little of it is now used for agriculture. The Gimpo Plain, one of the country's larger expanses of level arable land, covers much of the area of the cities of Gimpo and Bucheon.

The Capital Area has been home to a Korean capital for around 2,000 years. Its central location and relatively gentle landscape have given it a central role in the country's affairs.

The first capital to be constructed in the region was that of Baekje, one of the Three Kingdoms of Korea. The country's first capital was built in 19 BC and was named Wiryeseong. This is believed to have been constructed near the modern-day boundary of Seoul and Gwangju City. However, Baekje was unable to hold this territory, and surrendered the Han River valley to Goguryeo in the 5th century. The land was then taken over by Silla in the 6th century, at which point it came to play a critical role in helping Silla to establish ties with China.

After the fall of Silla, Taejo of Goryeo established the capital of his kingdom in Kaesŏng, now just north of the Demilitarized Zone. During the Mongol invasions of Korea in the 12th century, the seat of government briefly shifted to Ganghwa Island, now just south of the DMZ in Incheon metropolitan city, where the Mongol naval attacks were repelled for about a decade before the king voluntarily surrendered to stop the carnage the Mongols committed in the peninsula, in order to lure the king out.

After the fall of Goryeo in 1394, the capital moved to Seoul (then called Hanseong or Hanyang), staying within the same region. During the new dynasty's rule, extensive road systems, administrative buildings, royal palaces, and new ports were built, quickly attracting wealth from all over the kingdom. During the Korean Empire period, Hanseong's public transportation was improved with the installation of streetcars and manually drawn trolleys similar to taxis. Horse carriage systems similar to the ones in Europe were also established.

Following the Japanese annexation of Korea in 1910, Hanseong was renamed Keijo (Gyeongseong) and served as colonial Korea's capital. Upon Korea's liberation from Japan in 1945, the former colonial capital was renamed Seoul and became capital of South Korea.

In the Korean War (1950–1953), the Capital Area became the focus of battles so destructive that most of Seoul and the surrounding regions were eradicated. Seoul was especially hit hard, since it exchanged hands four times during the course of the war.

During the latter half of the 20th century, the Capital Area began to rapidly develop as South Korea's economic wealth expanded. Population expanded fourfold since the Korean War. In 2001, the new Incheon International Airport took over all international flights to Seoul.

Covering only about 12% of the country's area, the Seoul Capital Area is home to more than 48.2% of the national population, and is the world's third largest urban area. This percentage has risen steadily since the mid-20th century, and the trend is expected to continue. Currently more than half of the people who move from one region to another are moving to the capital area.[2] By 2020, it is projected that more than 52% of South Korea's population will live within the area, or 25,520,000 people.[3]

Various agencies have been set up to deal with the intergovernmental problems of the region. Proposals for consolidating some or all of the cities of the capital area into a handful of metropolitan cities have thus far not been implemented.

The Seoul Capital Area is divided among the special city of Seoul, the metropolitan city of Incheon, and province of Gyeonggi-do. Seoul has 25 gu (local government wards), Incheon has 8 gu and 2 counties, and Gyeonggi-do has 27 cities and 4 counties as the subdivisions.

The cities of the capital area are tightly interconnected by road and rail. Many of the country's railroad lines, most notably the Gyeongbu Line, terminate in the region. In addition, the needs for commuter rail are served by the Seoul Metropolitan Subway, which passes not only through Seoul and Incheon, but also through most of the outlying cities.

In addition, the region is a nexus for travel by air and water. The country's two largest airports, Incheon International Airport and Gimpo Airport, are both located in the metropolitan area. International and domestic ferries depart from Incheon's various ferry terminals several times a day; in addition, massive volumes of international freight pass through the container terminals of Incheon (primarily bound to and from China).

^A government publication states that on 1 November 2010, the population of “Seoul Metropolitan Area” stood at 23,616 thousand, which is the sum of the figures given for Gyeonggi-do (11,270 thousand), Seoul (9,708 thousand) and Incheon (2,638 thousand), apparently including the periphery.
Source: “Preliminary Results of the 2010 Population and Housing Census” (PDF). Statistics Korea. 21 January 2011. Retrieved 23 July 2011.